The present invention relates to large core plastic optical fiber and more particularly to offset clips for mounting and supporting such fiber.
Large core plastic optical fiber, often known as light fiber, is a product used in lighting applications. Light fiber is known as large core because it has a very large diameter compared to conventional optical fibers used for communications. Light fibers generally range from about 5 mm to about 18 mm in diameter. Bundles of smaller fibers are sometimes used instead of a single large fiber. Such bundles provide lower packing densities and result in greater insertion loss than single large fibers. Furthermore, extraction from bundled fibers is less efficient than from single large fibers. Therefore, single large fibers are generally preferred for lighting applications.
Light fiber has many uses both in decorative and functional lighting. Light fiber is generally broken into two categories known as end-light and side-light. End-light fibers are optimized for the efficient transportation of light with low absorption and low loss so that almost all of the light inserted into the fiber at one end emerges at or near the other end of the fiber. Side-light fiber, on the other hand, is optimized to emit light laterally along the entire length of the fiber. Preferably, side-light fiber will provide substantially uniform emission over the length of the fiber. For these purposes, generally uniform means uniform in appearance to the human eye. Over relatively long expanses, for example 20 meters or more, an intensity ratio of three to one from one end to the other will appear uniform to most people, as long as there are no abrupt changes in intensity. In addition, it is possible to combine end-light and side-light fibers so that an end-light fiber emits light from its end into a side-light fiber which then provides uniform emission over a distance. Such an arrangement makes it possible to separate the actual light source from the area to be illuminated.
There are many reasons why light fiber is advantageous over conventional lighting systems. For example, it may be used in remote source lighting. In remote source lighting the actual area to be lit is physically separated from the light source. This is useful for refrigerated areas because the heat emitting light source does not need to be located inside the refrigerated area. Remote source lighting is also useful in areas where explosion is a risk because the electrical components and heat emitting components are located outside of the hazardous area. Remote source lighting is advantageous in underwater lighting as well because the electrical components may be isolated from the water. Remote source lighting is also useful for lighting areas that are difficult to reach. The light source may be placed in a convenient location to simplify maintenance, while the fiber delivers light to the more difficult to reach location.
Side-light fibers also provide advantageous replacement of other types of conventional lighting. For example, side-light fiber may be used as a much more durable replacement for neon lights. Besides not being subject to breakage like neon lights, light fiber avoids the expense of custom glass bending and glass blowing associated with neon light fixtures. Furthermore, light fiber may be used to provide lighting effects unobtainable with neon. For example color wheels may be used to provide light fixtures having neon-like appearance while providing changing colors. By using two color wheels inserting different colors at each end of a light fiber a variety of effects may be achieved by the color mixing from the two light sources.
A variety of techniques may be used to manipulate the light distributed from light fiber. These are generally known as extraction techniques. U.S. Pat. Nos. 5,432,876, 5,659,643 and 5,845,038, the teachings of which are incorporated herein by reference, teach notching the fiber so that light is extracted from the fiber by total internal reflection from the notches. Published PCT application WO 00/25159 teaches the incorporation of various reflective materials, such as titanium dioxide, into the fiber clad in order to enhance both the extraction and the uniformity of the light emission. A light fiber according to this application is sold by 3M Company under the name HL Fiber.
Because of its flexible nature, it is necessary to support light fiber for viewing. A common way of doing so is to clamp the light fiber in a channel. Commonly assigned, copending U.S. patent application 09/969,272, the teaching of which is incorporated herein by reference, teaches a channel for supporting light fiber.
Channels are primarily useful if substantial lengths of the light fiber are to be displayed in straight lines. If the light fiber is to be displayed in a curved configuration, smaller offset clips are typically used to support it. Offset clips are particularly useful when the light fiber is used for neon replacement. Commonly used offset clips are very similar to the ones used to support neon light fixtures. Such offset clips are generally made of transparent, rigid plastic and formed in three parts. One part is a base or foot that accommodates a screw or other mechanical fastener for attaching the base to a wall or other surface. The second part, offset from the screw, is a post. A third part, with curved portion on the top forms a bracket that accommodates the neon tube or light fiber and clamps it into place. The two latter parts snap together and are biased apart by a spring. The spring provides resiliency that helps to protect a fragile neon tube. A problem with such brackets is that, in order to hold the light fiber in place, these brackets tend to pinch the fiber quite tightly. This can compress the fiber slightly causing undesirable extraction effects. This extraction can cause bright spots or other nonuniformities in the light output. Furthermore, the foot, although accommodating the fastener for attaching the offset clip to a wall, is unaesthetic in appearance.
According to the invention, an offset clip for use with light fiber has a base including a hole for accommodating a fastener. The clip also includes an insert with a light fiber retaining member. The light fiber retaining member may take any of several forms and may be either rigid or flexible. The insert and the base are held rotatably together by a locking mechanism. The insert and the base are arranged such that when the insert is inserted into the base, the insert hides the fastener from view